Tunable magnetrons



1957 c. c. AMSDEM ET AL 2,811,670

TUNABLE MAGNETRONS Filed Oct. 22, 1954 2 Sheets-Sheet l HEATER VOLTAGE SUPPLV lNl/ENTORS CHESTER C. AMsDE/v CARLTON 6. LEH/Z A TTO/2NEY 0 1957c. c. AMSDEM ETAL 2,811,670

TUNABLE MAGNETRONS Filed Oct. 22. 1954 2 Sheets-Shet 2 /NVENTORS CHESTERC. AMsDE/v CARLTON G. LEM/2 A TTORNEV United States, Patent 9 TUN ABLEMAGNETRONS Chester C. Amsden, Lexington, and Carlton G. Lehr, Waltham,Mass, assignors to Raytheon Manufacturing Company, Waltham, Mass., acorporation of Delaware Application October 22, 1954, Serial No. 464,229

Claims. (Cl. 315-39.61)

This invention relates to electron discharge devices, and, inparticular, to microwave magnetron discharge devices having variabletuning structures.

It has'been found desirable for certain purposes to be able tomechanically tune or change the output frequency of electron dischargedevices of the magnetron type, while such devices are in operation.Structures have previously been devised for the accomplishment of suchresults by the use of a diaphragm structure between the movable tunersection and the stationary member of the magnetron. In such structures atuning member is mechanically movable with respect to the resonantcavities of the magnetron. In order to maintain a hermetic seal insidethe envelope and at the same time permit movement or adjustment of thetuning member, a flexible diaphragm is sealed to the inner wall of thestationary structure and also sealed around the movable tuning member."It is essential that the heat which is developed by circulating R. F.currents in the tuning member of the magnetron be conducted away. Ifthis heat is not removed, the temperature of the tuner will rise untilgas detrimental to the operation of the tube is emitted and insome casesmelt the tuner. The difiiculty in conducting heat away from the tunerarises from the fact that the tuner is in a vacuum and is movable.Cooling is usually accomplished by passing a liquid against thediaphragm section exposed to atmospheric pressure, thereby conductingthe heat away.

I The diaphragm type of construction is very satisfactory inapplications where the frequency of the magnetron is varied infrequentlyand the total mechanical linear distance that the tuner is moved is keptvery small. Even in tubes having the LC type of tuners, which isrecognized by those skilled in the art as giving the greatest frequencyvariation for the smallest linear change of the tuner, the total linearchange of the tuner necessary to give the frequency variations capableof being produced by the modern magnetrons will cause the diaphragm tobreak due to fatigue long before the normal tube life has expired. Alater improvement on this type of tube has been to substitute a bellowstype of construction for the diaphragm. The action of the bellows isvery similar to the action of the diaphragm with the added advantagethat greater linear movement of the tuner can be had. The bellows iscooled by a coolant in a similar manner as the diaphragm is cooled bycirculating the coolant on that side of the bellows open to theatmosphere. In both the diaphragm and bellows type of construction it isimpossible to rapidly change the frequency of the magnetron by movingthe tuner due to the heavy weight of tuner plus coolant and the largeunbalance caused by the moving coolant.

It is an object of this invention, therefore, to devise a means forcooling the tuner of a tunable magnetron wherein the tuner is to bevaried at a rapid rate over the frequency outputrange of the magnetron.Another object is to accomplish the aforesaid object in a cheap andsimple manner wherein the weight of the tuning member is not increasedand the total movement of the tuning member is not limited by thecooling means.

The foregoing and other objects of the present invention will be bestunderstood from the following description of an embodiment of theinvention, reference being made to the accompanying drawings wherein:

Fig. l is a cross-sectional view of a tunable electron discharge deviceillustrating an embodiment of the invention;

Fig. 2 is a detailed view of Fig. 1 illustrating the con nection betweenthe cooling members and the tuning structure;

Fig. 3 is a detailed view of Fig.1 illustrating the connection betweenthe cooling members and the anode structure;

Fig. 4 is a top view of an embodiment of a cooling device;

Fig. 5 is a section 55 of Fig. 4; an

Fig. 6 is a section 6-6 of Fig. 1.

Referring now to Figs. 1, 2, 3 and 6, there is shown anelectron-discharge device of the magnetron tube type comprising an anodestructure 10, a cathode structure 11, and magnetic means 12 forestablishing a magnetic field in the direction perpendicular to the pathof electron flow between said cathode and anode structures. anodestructure 10 has .a cylindrical hole 13 centrally located therein.Extending radially inward from the sides of said anode 10 is a pluralityof anode vanes 14 which are positioned symmetrically about the axis ofsaid hole 13. As illustrated, the anode vanes 14 are substantially"rectangular members of conductive material, such as copper, which arerigidly secured to the anode structure 10 and which extend to a pointsomewhat short of the axis of hole 13. The lower edges of anode vanes 14are alternately connected by conductive straps 15 to prevent operationof the device in spurious modes. The lower end of hole 13 is covered byan end plate 16, which is attached to anode structure 10. Positioned onplate 16 and extending through an aperture therein is a lower magneticpole piece 17. Extending through an aperture in pole piece 17 is thecathode structure 11 which is cylindrical in form, and is positionedaxially in hole 13. The cathode structure 11 comprises a supportcylinder 18 coated with electron emissive material at the point wheresaid cylinder passes between the ends of anode vanes 14. The upper endof cylinder 18 is connected to a conductive hat 19, the edges of whichextend out beyond the electron emissive material coat on cylinder 13. Acylinder 29 surrounds and engages the cathode cylinder 18 below theelectron emissive portion. Cylinder 20 in cooperation with hat 19substantially prevents movement of electrons from the cathode structure11 in a direction axially of the hole 13. Cylinder 20 extends throughthe aperture in lower pole piece 17 and is spaced therefrom. Cylinder 20is attached to a lower support member 21, which is connected through aglass support seal 22, coaxial with support member 21 through a metalliccylinder 23 which, in turn, is rigidly connected to lower pole piece 17.Support member 21, part of which is hollow, contains a conductor thereinwhich is insulated and supported by ceramic seal 24. Said innerconductor is connected to one end of a cathode heater 25, which ispositioned inside the cathode cylinder 18 adjacent the electron emissivecoating. The other end of said heater 25 is connected to the end hat 19.The details of the cathode structure are illustrated and describedherein by way of example only, it being understood that any desiredcathode structure may be used.

Extending downward into the cavity formed by th anode vanes 14 is aplurality of tuner elements 26 which Fatented Oct. 29, 1957' The issupported by the body of a tuner structure 27. The tuner structure 27comprises an upper ring 28 to which the tuner elements 26 are attached.The tuner structure 27 is rigidly attached to a movable magnetic polepiece 29, which is shown in the fully retracted position. The pole piece29 is free to slide within the magnetic cylindrical structure 30 towhich the magnetic means 12 is attached. The magnetic pole piece 29 iscapable of being moved along the axis of hole 13. A vacuum seal ismaintained between the magnetic pole piece 29 and the outside atmosphereby means of a bellows arrangement 31. The bellows 31 is sealed at thepole piece 29 and also at the upper end of moving means 32, whichconsists of a threaded shaft 33 and a knob 34. It is clearly understoodthat the type of bellows arrangement and tuner support structure may beof any desired type.

In order to cool the tuning structure 27, two flexible cooling members35 of good conducting material are rigidly connected between pole piece29 and anode structure 10. The heat generated in the tuning structure 27is conducted through the cooling members 35' and thence into the anodeblock which acts as a heat sink. The cooling members 35 are constructedin the form of a spider having eight legs 36, as shown in Figs. 4 and 5.The periphery of legs 36 are rigidly connected to anode 10, as shown inFig. 3, while the central opening 37 is connected to the movable polepiece 29, as shown in Fig. 2. The legs 36 are constructed in the form ofa U in order to allow the greatest possible movement of the tuningstructure 27. The specific embodiment of the cooling structureillustrated in Figs. 4 and is shown in a complete electron dischargedevice illustrated in Fig. 1. border to provide sufficient cooling meansand also have great strength over repeated cyclings of the moving means32, two cooling members 38 and 39 have been used. Each cooling member 38and 39 has been constructed of unannealed copper having a thicknesspreferably no greater than 0.005 of an inch. This particular type ofconstruction allows the moving means 32 of the tuning structure 27 to becycled very rapidly without causing failure of the cooling members 38and 39 due to fatigue.

Fig. 2 shows a detailed view of how cooling members 38 and 39 areconnected to pole piece 29. Good heat transfer between the pole piece29, the tuner element 26, and the cooling members 38 and 39 is achievedby using five washers 40 constructed of good conducting material, onewasher placed on each external side of each cooling member and threewashers placed intermediate the cooling members. The cooling members 38and 39 and the five washers 40 are silver soldered to each other and tothe pole piece 29 and ring 28. Fig. 3 is a detailed view illustratinghow cooling members 38 and 39 are rigidly connected to the anode block10. Good heat transfer is assured from the cooling members 38 and 39into the anode block by means of five washers 41 constructed of goodconducting material, one placed on each external side of the coolingmembers and three washers placed intermediate the cooling members. Thecooling members 38 and 39 and the five washers 41 are silver soldered toeach other and to the anode block 10.

A signal output structure 42 is provided comprising a pick-up loop 43extending into one of the cavities between the anode vanes 14. One endof loop 43 is connected to the anode block 10 and the other end of loop43 extends out through a hole in the anode block 10 to form the centralconductor 44 of a coaxial line. A vacuum seal is provided between thecentral conductor 44 and an outer conductor 45 of said line which issealed in the anode block 10.

When a suitable heater voltage is applied to the anode heater, by meansof a heater voltage supply 46, and a suitable high voltage is appliedbetween the cathode and anodexby means of a high voltage supply 47, thedevice will oscillate at a frequency determined by the dimensions of thecavities formed between anode vanes 14 and the relative position of thetuner elements 26 as determined by the position of the tuner structure27. The tuner elements 26 are shunted together by means of a conductivestrap 48 to prevent spurious oscillations. The particular elementsillustrated herein are constructed to form what is called an LC tuner.This type of tuner is recognized as giving the greatest frequencyvariation for a given linear displacement of the tuning vanes in aresonant cavity. However, any other desiredv type of tuning may be usedsuch as, for example, slug or, inductance tuning, or as is used here, acombination of inductance and capacitance tuning.

This completes the description of the particular embodiments of. theinvention illustrated herein. However, many modifications thereof willbe apparent to persons skilled in the art without departing from thespirit and scope of this invention. For example, any desired magnetronanode configuration may be used. The tuner structure is not necessarilylimited to the cavity structure illustrated herein. There may be one ormany cooling members, each cooling member having a plurality of legsconsistent with good engineering, practices. The shape of the coolingmembers is not necessarily limited to a U form but may be constructed ofany shape depending only on the total movement of the tuning structureused and the amount of heat to be dissipated. Accordingly, it is desiredthat this invention be not limited by the particular details describedherein, except as defined by the appended claims.

What is claimed is:

I. An electron discharge device comprising a cathode, an anode structurespaced from said cathode, said anode structure defining a cavityresonator having a plurality of cavities, a tuning structure comprisinga plurality of tuning elements movably positioned with respect to saidcavity resonator, means adjacent said anode structure for producing amagnetic field in the space between said cathode and said anode, meansfor moving said tuning element of said tuning structure into and out ofsaid anode resonator, a movable sealing means for sealing the tuningstructure, and a separate means for cooling said tuning structure.

2. An electron discharge device comprising a cathode, an anode structurespaced from said cathode, said anode structure defining a cavityresonator having a plurality of cavities, a tuning structure comprisinga plurality of tuning elements movably positioned with respect to saidcavity resonator, a member of magnetic material positioned adjacent saidcavity resonator and movable with respect thereto, means for moving saidtuning element of said tuning structure into and out of said anoderesonator, means for moving said magnetic material in the same manner asthe tuning structure is moved, a bellows arrangement for sealing thetuning structure, and a separate means for cooling the tuning structureand said magnetic material member.

3. An electron discharge device comprising a cathode, an anode structurespaced from said cathode, said anode structure defining a cavityresonator having a plurality of cavities, a tuning structure comprisinga plurality of tuning elements movably positioned with respect to saidcavity resonator, means adjacent said anode structure for producing amagnetic field in the space between said cathode and said anode, meansfor moving said tuning element of said tuning structure into and out ofsaid anode resonator, a movable sealing means for sealing the tuningstructure, and a separate flexible conducting member connected betweensaid tuning structure and said anode for cooling said tuning structure.

4. An electron discharge device comprising a cathode, an anode structurespaced from said cathode, said anode structure defining a cavityresonator having a plurality of cavities, a tuning structure comprisinga plurality of tuning elements movably positioned with respect to saidcavity resonator, means adjacent said anode structure for producing amagnetic field in the space between said cathode and said anode, meansfor moving said tuning element of said tuning structure into and out ofsaid anode resonator, a movable sealing means for sealing the tuningstructure, and: a separate conducting mem'ber hav ing both a centralopening wherein the tuning structure is connected and a plurality oflegs having a U-shaped form for flexibility which are fiastened to theanode for cooling said tuning structure.

5. An electron discharge device comprising a cathode, an anode structurespaced from said cathode, said anode structure defining a cavityresonator having a plurality of cavities, a tuning structure comprisinga plurality of tuning elements movably positioned with respect to saidcavity resonator, a member of magnetic material positioned adjacent saidcavity resonator and movable with respect thereto, means for moving saidtuning element of said tuning structure into and out of said anoderesonator, means for moving said magnetic material in the 7 same manneras the tuning structure is moved, a bellows arrangement for sealing thetuning structure, and a separate conducting member having both a centralopening wherein the tuning structure is connected to the magneticmaterial and a plurality of legs having a U-shaped form for flexibilitywhich are fiastened to the anode for cooling said tuning structure andsaid magnetic material.

No references cited.

